'\" et
.TH TSORT "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
tsort
\(em topological sort
.SH SYNOPSIS
.LP
.nf
tsort \fB[\fIfile\fB]\fR
.fi
.SH DESCRIPTION
The
.IR tsort
utility shall write to standard output a totally ordered list of items
consistent with a partial ordering of items contained in the input.
.P
The application shall ensure that the input consists of pairs of items
(non-empty strings) separated by
<blank>
characters. Pairs of different items indicate ordering. Pairs of
identical items indicate presence, but not ordering.
.SH OPTIONS
None.
.SH OPERANDS
The following operand shall be supported:
.IP "\fIfile\fR" 10
A pathname of a text file to order. If no
.IR file
operand is given, the standard input shall be used.
.SH STDIN
The standard input shall be used if no
.IR file
operand is specified, and shall be used if the
.IR file
operand is
.BR '\-' 
and the implementation treats the
.BR '\-' 
as meaning standard input.
Otherwise, the standard input shall not be used.
See the INPUT FILES section.
.SH "INPUT FILES"
The input file shall be a text file.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR tsort :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments and input files).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
The standard output shall be a text file consisting of the order list
produced from the partially ordered input.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
Successful completion.
.IP >0 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
The
.IR LC_COLLATE
variable need not affect the actions of
.IR tsort .
The output ordering is not lexicographic, but depends on the pairs of
items given as input.
.SH EXAMPLES
The command:
.sp
.RS 4
.nf

tsort <<EOF
a b c c d e
g g
f g e f
h h
EOF
.fi
.P
.RE
.P
produces the output:
.sp
.RS 4
.nf

\fBa
b
c
d
e
f
g
h\fR
.fi
.P
.RE
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 8" ", " "Environment Variables"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
